The present invention relates to a developing device used in an electronic copying apparatus, more specifically to a developing device capable of supplying developers of two different kinds.
In the field of electronic copying apparatuses, there have recently been provided developing devices in which developers of two different kinds, e.g., developers with two different colors, are stored in a receptacle, and are selectively supplied to an electrostatic latent image formed on a photosensitive layer so that the image may be developed in two colors.
With use of one such conventional developing device, the quantity of one developer supplied for developing operation may be different from that of the other. Accordingly, the ratio between the quantities of the two developers stored in the receptacle varies as the developing operation advances. Namely, one developer may be used up, while the other remains in the receptacle. Further, the change of the ratio in quantity may exert a bad influence upon picture density. Thus, it is necessary to supply the developers individually on the basis of their consumption during the developing operation.
To meet this requirement, the prior art developing device is so constructed that resupply hoppers are provided individually for the developers, and have their respective supply rollers. In such an arrangement, required quantities of the developers are fed individually into the receptacle by selectively rotating the supply rollers on the basis of the consumption of the developers or the residual quantities thereof in the receptacle.
Having such construction, the prior art developing device is bulky and requires a wide setting space, thus leading to an increase in size of the copying apparatus. The conventional device also requires a substantial number of components or members, resulting in an increase in cost.